Referring to FIG. 1, a conventional camera 10 typically comprises a lens 12 mounted between a threaded arrangement 14 disposed in a plastic mount 16. The mount 16 is mounted at one end on a PCB board 17 and a semiconductor photosensor 18 (e.g. charge-coupled device CCD or photodiode or CMOS, linear or area imaging array) is mounted in turn on the PCB board 17 at a location enclosed by the mount 16. In use, the position of the lens 12 relative to the photosensor 18 is adjusted (by adjusting the position of the threaded arrangement 14) to cause light travelling through the lens 12 to be focused on the photosensor 18.
Recent years have seen the inclusion of cameras into handheld personal devices (e.g. mobile phones). At the same time, intense price competition has led to a drive to reduce the cost of cameras, by reducing the number of components therein. This has resulted in the development of the “no-focus” or “focus-free” camera. Referring to FIG. 2, a no-focus camera 20 comprises a lens 22, mount 24 (mounted on a PCB board 25) and semiconductor photosensor 26 (in a similar fashion to the conventional camera depicted in FIG. 1). However, the lens 22 is directly mounted and/or bonded to the mount 24, without the inclusion of a threaded arrangement therebetween. In this case, it is no longer possible to move the lens in the mount to focus light onto the photosensor 26. Accordingly, it is necessary to manufacture the lens with a very precise (i.e. with very low tolerances) predefined focus, so that when the components of the no-focus camera are assembled, the lens precisely focuses light on the photosensor.
There exists a need in the art for determining whether the lens in a no-focus camera like that of FIG. 2, or of other types of camera, is correctly focused. Similarly, there is a need in the art for a useful mechanism to determine the distance at which the camera is focused.